Acrylic rubbers are used as functional parts, security parts, and the like centralized in the surrounding of the engine of automobiles due to their characteristics such as heat resistance and oil resistance.
However, curing of the acrylic rubber involves problems that processability is poor because the rubber adheres to a roll in kneading with additives such as a filling agent and a vulcanizing agent, is hardly smoothed on sheeting, or is non-flowable on molding and that curability is poor because vulcanization speed is slow or post-cure for a long time is required. Further, there are many problems such as poor reliability and the necessity of high-precision processing of flange face when the acrylic rubber is used as a seal.
Acrylic ribbers in which processability and curability were improved are reported (Patent Document 1), but they cannot be cured by photo curing which enables rapid curing, resulting in failure to improve productivity.
Design of a polymer having large molecular weight between crosslinking points is required for obtaining satisfactory rubber elasticity and elongation of a cured article. The present inventors have hitherto reported a polymer wherein its main chain is an acrylic polymer obtained by living radical polymerization and which has a (meth)acryloyl group at its end (Patent Documents 2 and 3).
However, there is apprehension that a polymer having large molecular weight is high in viscosity and workability is inferior. Further, when a reinforcing filler such as Aerosil is added to an acrylic polymer not having adequate strength, there is a problem that viscosity is further increased.
Technology with respect to the combination use of radical photopolymerization and cationic photopolymerization has been reported (Patent Documents 4 and 5), but there have not been reported a polymer having an acrylic polymer as a main chain and a material having heat resistance, weather resistance and oil resistance in good balance.    Patent Document 1: JP-A-2000-154370    Patent Document 2: JP-A-2000-72816    Patent Document 3: JP-A-2000-95826    Patent Document 4: JP-A-5-117592    Patent Document 5: JP-A-8-143755